Re: [PATCH net-next] virtio-net: switch napi_tx without downing nic

[Zhu Yanjun <yanjun.zhu@linux.dev>]

在 2023/12/21 13:20, Heng Qi 写道:
>
>
> 在 2023/12/21 上午11:02, Zhu Yanjun 写道:
>> 在 2023/12/20 16:07, Heng Qi 写道:
>>> virtio-net has two ways to switch napi_tx: one is through the
>>> module parameter, and the other is through coalescing parameter
>>> settings (provided that the nic status is down).
>>>
>>> Sometimes we face performance regression caused by napi_tx,
>>> then we need to switch napi_tx when debugging. However, the
>>> existing methods are a bit troublesome, such as needing to
>>> reload the driver or turn off the network card. So try to make
>>> this update.
>>
>> What scenario can trigger this? We want to make tests on our device.
>
> Hi Zhu Yanjun, you can use the following cmds:
>
> ethtool -C tx-frames 0, to disable napi_tx
> ethtool -C tx-frames 1, to enable napi_tx


Thanks a lot. Just now I made tests on our device. I confirmed that 
virtion_net driver can work well after running "ethtool -C NIC tx-frames 
0 && sleep 3 && ethtool -C NIC tx-frames 1".

You can add "Reviewed-and-tested-by: Zhu Yanjun <yanjun.zhu@linux.dev>"

Thanks,

Zhu Yanjun

>
> Thanks.
>
>>
>> Zhu Yanjun
>>
>>>
>>> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
>>> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>>> ---
>>>   drivers/net/virtio_net.c | 81 
>>> ++++++++++++++++++----------------------
>>>   1 file changed, 37 insertions(+), 44 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index 10614e9f7cad..12f8e1f9971c 100644
>>> --- a/drivers/net/virtio_net.c
>>> +++ b/drivers/net/virtio_net.c
>>> @@ -3559,16 +3559,37 @@ static int 
>>> virtnet_coal_params_supported(struct ethtool_coalesce *ec)
>>>       return 0;
>>>   }
>>>   -static int virtnet_should_update_vq_weight(int dev_flags, int 
>>> weight,
>>> -                       int vq_weight, bool *should_update)
>>> +static void virtnet_switch_napi_tx(struct virtnet_info *vi, u32 
>>> qstart,
>>> +                   u32 qend, u32 tx_frames)
>>>   {
>>> -    if (weight ^ vq_weight) {
>>> -        if (dev_flags & IFF_UP)
>>> -            return -EBUSY;
>>> -        *should_update = true;
>>> -    }
>>> +    struct net_device *dev = vi->dev;
>>> +    int new_weight, cur_weight;
>>> +    struct netdev_queue *txq;
>>> +    struct send_queue *sq;
>>>   -    return 0;
>>> +    new_weight = tx_frames ? NAPI_POLL_WEIGHT : 0;
>>> +    for (; qstart < qend; qstart++) {
>>> +        sq = &vi->sq[qstart];
>>> +        cur_weight = sq->napi.weight;
>>> +        if (!(new_weight ^ cur_weight))
>>> +            continue;
>>> +
>>> +        if (!(dev->flags & IFF_UP)) {
>>> +            sq->napi.weight = new_weight;
>>> +            continue;
>>> +        }
>>> +
>>> +        if (cur_weight)
>>> +            virtnet_napi_tx_disable(&sq->napi);
>>> +
>>> +        txq = netdev_get_tx_queue(dev, qstart);
>>> +        __netif_tx_lock_bh(txq);
>>> +        sq->napi.weight = new_weight;
>>> +        __netif_tx_unlock_bh(txq);
>>> +
>>> +        if (!cur_weight)
>>> +            virtnet_napi_tx_enable(vi, sq->vq, &sq->napi);
>>> +    }
>>>   }
>>>     static int virtnet_set_coalesce(struct net_device *dev,
>>> @@ -3577,25 +3598,11 @@ static int virtnet_set_coalesce(struct 
>>> net_device *dev,
>>>                   struct netlink_ext_ack *extack)
>>>   {
>>>       struct virtnet_info *vi = netdev_priv(dev);
>>> -    int ret, queue_number, napi_weight;
>>> -    bool update_napi = false;
>>> -
>>> -    /* Can't change NAPI weight if the link is up */
>>> -    napi_weight = ec->tx_max_coalesced_frames ? NAPI_POLL_WEIGHT : 0;
>>> -    for (queue_number = 0; queue_number < vi->max_queue_pairs; 
>>> queue_number++) {
>>> -        ret = virtnet_should_update_vq_weight(dev->flags, napi_weight,
>>> - vi->sq[queue_number].napi.weight,
>>> -                              &update_napi);
>>> -        if (ret)
>>> -            return ret;
>>> -
>>> -        if (update_napi) {
>>> -            /* All queues that belong to [queue_number, 
>>> vi->max_queue_pairs] will be
>>> -             * updated for the sake of simplicity, which might not 
>>> be necessary
>>> -             */
>>> -            break;
>>> -        }
>>> -    }
>>> +    int ret;
>>> +
>>> +    /* Param tx_frames can be used to switch napi_tx */
>>> +    virtnet_switch_napi_tx(vi, 0, vi->max_queue_pairs,
>>> +                   ec->tx_max_coalesced_frames);
>>>         if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL))
>>>           ret = virtnet_send_notf_coal_cmds(vi, ec);
>>> @@ -3605,11 +3612,6 @@ static int virtnet_set_coalesce(struct 
>>> net_device *dev,
>>>       if (ret)
>>>           return ret;
>>>   -    if (update_napi) {
>>> -        for (; queue_number < vi->max_queue_pairs; queue_number++)
>>> -            vi->sq[queue_number].napi.weight = napi_weight;
>>> -    }
>>> -
>>>       return ret;
>>>   }
>>>   @@ -3641,19 +3643,13 @@ static int 
>>> virtnet_set_per_queue_coalesce(struct net_device *dev,
>>>                         struct ethtool_coalesce *ec)
>>>   {
>>>       struct virtnet_info *vi = netdev_priv(dev);
>>> -    int ret, napi_weight;
>>> -    bool update_napi = false;
>>> +    int ret;
>>>         if (queue >= vi->max_queue_pairs)
>>>           return -EINVAL;
>>>   -    /* Can't change NAPI weight if the link is up */
>>> -    napi_weight = ec->tx_max_coalesced_frames ? NAPI_POLL_WEIGHT : 0;
>>> -    ret = virtnet_should_update_vq_weight(dev->flags, napi_weight,
>>> -                          vi->sq[queue].napi.weight,
>>> -                          &update_napi);
>>> -    if (ret)
>>> -        return ret;
>>> +    /* Param tx_frames can be used to switch napi_tx */
>>> +    virtnet_switch_napi_tx(vi, queue, queue, 
>>> ec->tx_max_coalesced_frames);
>>>         if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL))
>>>           ret = virtnet_send_notf_coal_vq_cmds(vi, ec, queue);
>>> @@ -3663,9 +3659,6 @@ static int 
>>> virtnet_set_per_queue_coalesce(struct net_device *dev,
>>>       if (ret)
>>>           return ret;
>>>   -    if (update_napi)
>>> -        vi->sq[queue].napi.weight = napi_weight;
>>> -
>>>       return 0;
>>>   }
>